Refrigerated trucks of the semi-trailer type are utilized to supply various grocery stores, and there are numerous such trucks in operation across the country today. These trucks typically include a front freezer compartment for frozen foods and a rear refrigerated compartment for perishables. The compartments are separated by a bulkhead door, which can be moved to vary the relative sizes of the compartments in accordance with the particular load to be carried. It will of course be appreciated that the two compartments must be maintained at different temperatures. In addition, proper humidity must be maintained in the rear refrigerated compartment to keep the perishables fresh.
In the past, the common approach to meeting the different temperature requirements of the two compartments within such refrigerated trucks has been to provide an auxiliary or second refrigeration unit for the rear refrigerated compartment. This of course results in extra expense, control and maintenance problems, and other difficulties. In addition, the use of a separate refrigeration unit for the rear compartment removes moisture and thus lowers the humidity therein, which in turn affects freshness of the perishables and requires additional maintenance in terms of defrosting the evaporator of the unit. There are thus substantial drawbacks to the use of separate auxiliary refrigeration units for the rear refrigerated compartments of refrigerated trailer trucks.
Another approach to this problem has been to utilize thermostatically controlled fan kits in the bulkhead doors separating the compartments, instead of a separate refrigeration unit for the rear compartment. For example, U.S. Pat. No. 3,057,284 to Learmont shows a refrigerated trailer truck incorporating such a bulkhead door fan kit. There are, however, certain difficulties with this approach, one of which is the maintenance of proper temperature distribution within the rear compartment. Perishables located near the bulkhead tend to get too cold or even freeze, while those at the other end of the compartment tend to get too warm. Another problem is that such fan kits are usually supplied by electrical hook-ups which can be dislodged during loading or unloading, or not reconnected after movement of the bulkhead. If the bulkhead door is moved, extra care must be taken to assure that proper electrical connection and hook-up is maintained otherwise there will be little if any refrigeration to the rear compartment. Either of these can result in loss of at least some perishables from spoilage or freeze damage. Bulkhead door fan kits are therefore unsatisfactory for several reasons.
There is thus a need for a refrigeration/air exchanger unit which is not mounted in the bulkhead door but which draws some of the cold air from the freezer compartment by means of an improved themostatically controlled fan and heater arrangement for achieving proper temperature and humidity control in the refrigerated compartment without the expense and maintenance associated with a separate auxiliary refrigeration unit for that compartment.